Re: [Xen-devel] [PATCH] Don't attach needless options when launch pygrub

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

On Wed, 2010-07-14 at 08:29 +0100, Yu Zhiguo wrote:
> Hi Ian,
> 
> Ian Campbell wrote:
> > On Wed, 2010-07-14 at 07:15 +0100, Yu Zhiguo wrote:
> >> We should always run grub if bootloader is specified,
> >> options 'kernel' and 'ramdisk' are needless.
> > 
> > Not quite. If you specify both bootloader and kernel then this instructs
> > pygrub to extract the specific named file from the guest file system,
> > similarly for the ramdisk.
> > 
> 
>  Do you mean in this case, pygrub will use specified kernel
> that lie in the filesystem of the DomU?

I thought so, I looks like I was mistaken though.

>  I think this is good. But now pygrub's action is using the
> specified kernel in Dom0, but not run grub.

Hmm, pygrub is certainly run, regardless of having a kernel configured
or not. What is in question is what --kernel and --ramdisk actually
cause pygrub to do and whether that is useful.

As far as I can see the --kernel and --ramdisk options end up in the
incfg map which only used in a handful of places, most of which just
extract incfg["args"]. The only places which do not do this are the
calls to sniff_solaris and sniff_netware both of which appear to make
use of incfg["kernel"] (but not incfg["ramdisk"]).

So it looks like specifying the kernel option in addition to bootloader
is infact useful if you are booting a Solaris or Netware domU but is
harmless/ignored otherwise. I think we need to continue to support this
use case and I don't see any particular reason to force those users to
change their configuration file syntax for this issue (if it's even an
issue, I still don't really see the problem).

Perhaps it would be better to update pygrub so that --kernel actually
does something consistent in the non-{Solaris,Netware} case, such as
perhaps selecting the configuration entry with the match kernel path
instead of defaulting to entry 0? (e.g. make "-q --kernel=/boot/FOO"
select the entry with kernel /boot/FOO)

It looks like --ramdisk (and the associated plumbing through xend) may
in fact be useless at this time. I'd say it is harmless to plumb it
through for consistency though -- perhaps in the future pygrub (or
another bootloader) might want to use it.

Ian.


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